DESCRIPTION:(from applicant's abstract) It is now clear that motor cortical maps may undergo dynamic changes as new motor skills are acquired. Many studies have shown that the motor map of a body part may expand and become more excitable when that part is used in a new motor skill. Conversely, nearby, task-unrelated motor/muscle maps may shrink. The involvement of both excitatory and inhibitory processes has been shown, and the cellular mechanisms underlying these changes, including synaptic plasticity in intracortical horizontal connections, have been proposed. Significantly, however, we have as yet no clear understanding of how such changes in map size or configuration may contribute to the programming of new muscle synergies as a new skill is acquired. This application addresses this important problem. Using chronically implanted intracortical and EMG electrode arrays, we have tracked changes in the maps for task-related, single muscles, in the precentral (MI) motor cortex of an alert monkey, as it learned successive variants of a visuomotor, forelimb tracking task. Unexpectedly, we found that skill acquisition was marked by a fractionation of cortical muscle maps rather than an expansion. In addition, fractionated components of different muscle maps were observed to "move" into or out of spatial correlation with one another, as new tasks were acquired. We propose that such fractionation and re-assembly of MI muscle maps may contribute to and/or reflect the development of new muscle synergies during skill acquisition. Experiments are proposed here that will allow us to obtain new evidence for or against this hypothesis. In addition, we will examine: (a) the extent to which these learning induced changes in cortical muscle maps reflect intracortical as opposed to spinal sites of plasticity; (b) the extent to which changing cortical maps and related muscle synergies are reversible; and (c) the potentially confounding effects of repeated microstimulation in measuring cortical motor maps. Together, these experiments will provide important new evidence about the relationship between cortical map plasticity and the reprogramming of intramuscular coordination as new skills are acquired.